I. Field of the Invention
The present invention relates generally to fuel management systems for internal combustion engines and, more particularly, to such a fuel management system for use with an internal combustion engine utilizing a gaseous fuel as the fuel source.
II. Description of the Prior Art
In order to obtain optimum engine operation, modern day internal combustion engines of the type, for example, used in automotive vehicles, monitor the air/fuel ratio of the fuel charge to the engine and modify the air/fuel ratio to obtain desired engine performance. Careful monitoring of the air/fuel ratio is necessary to obtain best fuel economy, low engine emission and the like.
There is also a modern trend at employing gaseous fuels as the engine fuel. Such gaseous fuels include compressed natural gas (CNG), liquid natural gas (LNG) and liquid petroleum gas (LPG). The advantages of utilizing a gaseous fuel include lower emissions and cleaner combustion, better cold starting for the engine and less expensive fuels due to their abundant availability.
In order to monitor the air/fuel ratio for a gaseous fuel internal combustion engine typically an air/fuel ratio sensor, commonly known as an air/fuel ratio or oxygen sensor, is exposed to the exhaust gas stream ti-om the engine. The air/fuel ratio sensor provides an output signal to a control circuit indicative of the amount of oxygen in the exhaust gas stream, The amount of oxygen in the exhaust gas stream in turn is representative of the air/fuel ratio of the fuel charge to the engine.
One disadvantage of utilizing an air/fuel ratio sensor in the exhaust gas stream for the internal combustion engine is that the air/fuel ratio sensor is only capable of providing a feedback signal to the control system indicative of the air/fuel ratio. Consequently, the delay imposed between the engine combustion and the time in which the air/fuel ratio sensor determines the oxygen content in the exhaust gas stream and provides its signal to a control circuit results in less than optimum engine operating conditions, especially during changing engine operating conditions.